This invention relates generally to vehicle moisture detection systems which detect precipitation on an outer surface of a vehicle window or windshield and, more particularly, to a rain detector which is decoupled from the windshield and capable of detecting rain on an exterior surface of the window.
Several rain sensor systems have been proposed to date. Early systems were typically closely coupled to the interior surface of the windshield, such as by bonding to the glass surface or the like. By positioning the system immediately adjacent to the window, the rain sensor units sampled a relatively small area on the window. However, even the small sampling area may include many scratches, pits or other surface irregularities on the window which may dominate the signal received by the rain sensor system, thereby leading to an erroneous detection of rain on the window when little or no rain is actually present. Furthermore, in order to achieve an adequate sampling area, a greater number of sampling channels is required, which results in an increase of cost and bulk to the units. An additional concern with closely coupled units is that they create difficulties in the vehicle assembly plants, since it is then necessary to handle two different windshield configurations in the factory, which increases inventory costs. The close coupling also creates difficulties in the replacement of the windshield in the after market, since the rain sensor unit has to be replaced along with the windshield if the windshield is damaged.
Other rain sensor devices have been proposed that are decoupled from the windshield such that the sensors are spaced from the interior surface of the windshield, in order to avoid concerns with replacing the windshield and other deficiencies present with the coupled systems. However, by spacing the rain sensor from the interior of the surface of the window, the rain sensor receives data from a larger sampling area on the window. This further increases the likelihood of significant errors in detecting rain droplets on the exterior of the windshield and discerning them from scratches or other surface irregularities which may be present on the window. This is a greater concern when the rain sensor is operable on a windshield of a vehicle, since the exterior surface of a windshield is typically scratched and/or nicked in multiple places due to debris impacting the windshield as the vehicle is driven. Because the number of surface irregularities may be significantly greater than the amount of precipitation that may be present on the window, the rain sensor systems may result in erroneous detection of rain droplets when there is little or no precipitation present on the window.
Other systems have recently been proposed which include an illumination source and an illumination sensor at an acute angle relative to one another, such that when the light from the illumination source is refracted through the windshield and further reflected by water droplets on the exterior surface of the windshield, the light may be received by the illumination sensor and processed to determine if precipitation is present on the exterior surface of the windshield. However, the addition of an illumination source further intensifies the appearance of the surface irregularities which may be present on the window, since the light reflects and scatters from the pits or scratches back toward the sensor, such that there is a greater likelihood that the surface irregularities will dominate the signal received by the illumination sensor. This again may result in an erroneous detection of precipitation when there is little or no rain present on the window, since none of these systems account for any surface irregularities, such as scratches or pits or the like, on the exterior and/or interior surfaces of the window.
The present invention is intended to provide a vehicular rain sensor which accurately detects rain on a vehicle window under a wide variety of operating conditions, including when fog is present on the windshield interior, and provides the ability to separately detect the presence of rain or fog on a window of a vehicle.
According to one aspect of the present invention, a rain sensor which senses precipitation at a vehicle window comprises an imaging array sensor directed toward a vehicle window for detecting precipitation at the window and a control which is responsive to the imaging array sensor detecting precipitation at the window. The control includes a filtering process. One function of the filtering process is to reduce the affect on the rain sensor of irregularities of the vehicle window, particularly surface irregularities of the window.
According to another aspect of the invention, the control may include a computer programmed with an edge detection algorithm, for detecting the edges of droplets of rain as they appear on the exterior surface of the windshield. The control may be coupled to a windshield wiper such that the wipers are turned on when a predetermined threshold value of precipitation is detected on the window. An illumination source may also be implemented for illuminating the window when ambient light levels are low. Preferably, the filtering process is operable to correct for signals due to surface irregularities when the illumination source is activated.
In one form, an optic may be included between the imaging array sensor and the windshield. The optic has a low f-ratio which provides a narrow depth of field to the imaging array sensor, such that only the area immediately adjacent the windshield is in focus on the imaging array sensor. The imaging array sensor and optic are oriented relative the windshield to satisfy the Scheimpflug condition such that the optic focuses an entire sampling area of the windshield onto the correspondingly angled imaging array sensor.
In another form, the vehicle rain sensor includes a polarizing filter that is at least occasionally positioned in an optical path between the illumination source and the sensor to filter out polarized light radiated from a fog particle on the inside of the window. The control responds to a signal from the sensor in order to indicate precipitation on an exterior surface of the window independent of moisture on an interior surface of the window.
According to still yet another aspect of the present invention, a vehicle rain sensor for detecting rain or fog on a vehicle window comprises at least one illumination source and at least one imaging sensor, defining at least one optic path therebetween. At least one of the optic paths is defined between at least one of the illumination sources and the vehicle window, and between the vehicle window and at least one of the imaging sensors. A polarizing filter is positioned along at least one of the optic paths, and a control responds to an output of at least one of the illumination sensors in order to indicate precipitation on an exterior surface of the window or fog on an interior surface of the window. The control includes a filtering process to account for irregularities such as surface irregularities of the vehicle window.
In one form, the control may communicate with the vehicle windshield wipers and/or the rear window wipers when rain is detected on the exterior surface of the window and communicate with a blower within the vehicle to activate the blower when fog is detected on the interior surface of the window.
According to another aspect of the present invention, a vehicular sensor is adaptable for receiving a signal through a vehicle window. The vehicular sensor comprises an imaging sensor directed at the window from inside the vehicle and a control. The control includes a filtering process to adjust an output of the imaging sensor in response to a plurality of signals in the output which are associated with surface irregularities on the vehicle window. The control then responds to an adjusted output of the imaging sensor.
The invention provides a new principle of detection which is decoupled from the windshield and may accurately detect the presence of rain on the windshield and distinguish rain from other phenomena which could be confused with rain, such as fog or surface irregularities associated with the window. The invention further optimizes rain sensing by filtering the signal from the sensor to account for the surface irregularities on the window, thereby substantially precluding the likelihood of a false rain detection by the sensor. The invention may also accurately provide for the separate detection of fog, thereby allowing further measures to be taken to improve driver visibility.